Field of the Invention
The present inventions relate to power transmitting apparatuses which can arbitrarily and/or selectively transmit or cut off driving power of an engine to or from wheels of a vehicle.
Description of the Related Art
Some conventional power transmitting apparatuses (“automatic transmissions”) for motor vehicles include a torque converter (so-called “torque converter type” starting system) and some include a starting clutch (so-called “start-clutch type” starting system). In the torque converter type automatic power transmitting apparatuses, it is possible to improve the starting performance at the time of start due to the torque amplification function of the torque converter. On the other hand, in the start-clutch type automatic power transmitting apparatuses, it is possible to improve the power transmitting efficiency since it does not have slippage during the steady running of vehicle which is caused by the apparatus of the torque converter type.
As described above, in the torque converter type automatic transmission, although it has a technological advantage of improvement of the starting performance at the time of start due to the torque amplification function of the torque converter, it has a technological disadvantage of reduction of the power transmitting efficiency due to slippage of the torque converter. On the other hand, in the automatic transmission of the start-clutch type, although it has a technological advantage of improvement of the power transmitting efficiency during the steady running of vehicle since it does not have slippage peculiar to the torque converter type, it has a technological disadvantage of reduction of the starting performance since it does not have the torque amplifying function of the torque converter and thus it is necessary to increase the reduction ratio of the transmission to prevent reduction of the starting performance.
In order to solve these defects of the prior art, Japanese Patent Document JP 2010-84828 A describes a power transmitting apparatus which is provided with a clutch for switching a first power transmitting system for transmitting the driving power of the engine to wheels via a torque converter and a second power transmitting system for transmitting the driving power of the engine to wheels without via a torque converter and is able to satisfy both the functions of improving the starting performance due to the torque amplifying function of the torque converter and of improving the power transmitting efficiency during the steady running of vehicle.
Some motor vehicles include an idling-stop control for automatically stopping the engine when a vehicle is stopped in order to improve the fuel consumption. Additionally, some motor vehicles include a control for stopping fuel supply (fuel cutoff) to the engine when the engine speed is dropped below the idling rotation (hereinafter referred to as “economic-running control”). That is, the economic-running control improves fuel consumption by continuing the stop of fuel injection to the engine to reduce the fuel consumption until a vehicle is stopped when the engine rotational speed is dropped below the idling rotational speed while the vehicle is decelerated.
However, with such systems, the engine does not always restart upon restarting of fuel supply, for example, if fuel supply is restarted when the acceleration pedal depressed by a driver during the economic-running control is performed (that is, when the engine speed is in a state below the idling speed due to the fuel cutoff). That is, when the engine is in a rotational speed range (such a rotational speed range is hereinafter referred to as “assist-start range”) lower than a speed in which the engine can be started if fuel supply is restarted (such a rotational speed is hereinafter referred to as “self-start rotational speed”) and higher than a speed in which the engine cannot be started even if fuel supply is restarted and can be started only by a starter (such a rotational speed is hereinafter referred to as “starter-start rotational speed”), there would be caused a problem that the engine cannot be started until its rotational speed is dropped below the starter-start rotational speed and thus its restart response is impaired.
Japanese Patent Document JP 2012-97843 A describes switching the driving power of the engine to the second power transmitting system in which the driving power is transmitted to wheels without via the torque converter by actuating a lock-up clutch and to hold the engine at a speed higher than the self-start rotational speed or lower than the starter-start rotational speed. This reduces a length of the time of the assist-start range during the economic-running control and thus prevents deterioration of the engine restart response to some extent.